Hong Kong -LRB- CNN -RRB- -- Officials wielding infrared thermometers are becoming more difficult to avoid at entry points from mainland China as Hong Kong strengthens its defenses against the H7N9 strain of bird flu .

Extra measures are being taken this week during an expected surge in visitors across the border for the three-day Labor Day break from Monday to Wednesday .

Up to 600 officials will be stationed at border crossings during the holiday , including more than 100 volunteers in addition to government staff , according to Hong Kong 's food and health secretary , Ko Wing-man .

`` There will also be promotion and education work done at the borders reminding visitors to stay home or visit a doctor if they are not feeling well , '' he added , in response to reporters ' questions on Sunday .

Along with extra screening at entry points , tour operators are also being asked to keep an eye on travelers who may be showing symptoms of what the World Health Organization calls `` one of the most lethal influenza viruses '' it has ever seen .

As of Sunday , the number of bird flu infections had risen to 124 , based on provincial Ministry of Health websites . The figure includes one case in Taiwan , which remains the only recorded infection beyond mainland China .

Within the country , the infection has spread to eight provinces and the city of Shanghai , as well as the capital Beijing . Twenty-three people have so far died from the infection .

According to the last figures released from the national Ministry of Health on April 24 , 14 people have recovered after treatment . On that day , the ministry switched to weekly updates and the figure has n't been updated since .

Health authorities are still investigating the possible sources of infection and how the virus is spread . As recently as Thursday , the WHO repeated that so far there had been no evidence of sustained human-to-human transmission .

Taiwanese health officials say the territory 's first case was imported by a local businessman who regularly traveled between back and forth between China 's Jiangsu province and Taiwan .

To date , 27 cases have been reported in Jiangsu , resulting in four deaths . That 's only the second highest number of provincial cases behind Zhejiang , which has reported 46 cases of infection and six deaths .

Wearing a customary white lab coat during a tour of the China 's Center for Disease Control and Prevention on Sunday , Premier Li Keqiang urged officials to be vigilant against bird flu .

`` We can not afford to take it easy or relax , as we are facing a new virus . We should be prepared for any possible development , '' he said in quotes carried by state-run news agency Xinhua .

On Saturday , a mass cull was ordered at a major wholesale poultry market in the city of Dongguan after random testing detected the presence of an H7 strain of bird flu . No birds were showing symptoms , according to a statement from the city 's Bureau of Agriculture . Nor had been there been any cases of human infection , it added . Dongguan is a city in the central province on Guangdong .

Hong Kong has said it is prepared to halt the import of live poultry , meat and eggs if the H7N9 virus is found at a mainland poultry farm with export ties to Hong Kong , or if that farm is within 13 kilometers of another that supplies the city .

CNN 's Vivian Kam in Hong Kong and Feng Ke in Beijing contributed to this report .

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Hong Kong officials step up testing at entry points from mainland China

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Millions of Chinese expected to travel to Hong Kong for Labor Day break

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Infrared thermometers are used to detect higher temperatures in tourists

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Number of infection cases in China is 124 , including one in Taiwan